Conventionally, as a phosphor, yttrium aluminum garnet (YAG; Y3Al2(AlO4)3) has been known. In addition, YAG activated with Ce3+, YAG activated with a Ce phosphor or Tb3+, and a phosphor having a garnet structure such as a Tb phosphor have been known as high efficient phosphors. Such phosphors having a garnet structure have been used for many light-emitting devices (see, for example, PTL 1 and 2 and NPL 1).
A phosphor having a garnet structure that is activated with Ce3+ is excited when being irradiated with corpuscular beams or electromagnetic waves, and emits visible light in blue green to red (see, for example, NPL 1 and PTL 3).